1. Field of the Invention:
The present invention relates to edge-coating glasses, which optically have a low refractive index, have a marked absorption in the near infrared region and have excellent chemical durability for parasitic oscillation of laser glasses.
2. Description of the Prior Art:
Recently, a thin layer of a low melting point glass which has a slightly higher refractive index than that of a laser glass and absorbs well laser light of a wavelength of 1.06.mu. has been applied to the circumferential edge of a laser glass disk in order to prevent reflection and scattering of laser light to improve the oscillation characteristics.
For this purpose, although a low melting point glass has been employed in U.S. Pat. No. 4,060,422 (corresponding to Japanese Patent Application (OPI) 69917/77) (The term "OPI" as used herein refers to a "published unexamined Japanese patent application".), this low melting point glass has not only the defect of a low chemical durability, which is a general characteristic of a low melting point glass, but also a low absorption coefficient of light of a wavelength of 1.06.mu.. Consequently, the laser light passes through the thin layer of the low melting point glass, is reflected at the interface of the air and the layer and passes again into the laser glass. As a result the oscillation characteristics have not been sufficiently improved yet.